Combustion chamber assembly in a gas turbine engine

ABSTRACT

Overrich regions of fuel mixture in the combustion chamber of a gas turbine engine are dispersed by a jet of air directed into the region. Plumes of fuel/air mixture from adjacent airspray burners overlap to create overrich regions which tend to produce soot. Aligned apertures in the head of the combustion chamber direct jets of high pressure air at the regions with as little loss of momentum as possible, to disperse them. The apertures may be in the form of slots to provide fan-shaped jets.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a combustion chamber assembly in a gas turbineengine.

2. Description of Related Art

One configuration of combustor chamber assembly includes an annularcombustion chamber with a number of airspray burners arranged within it.Each burner introduces a mixture of fuel and air into the combustionchamber. The fuel droplets or vapour extend into the chamber as a plume.At a point downstream of the burner the plumes produced by adjacentburners overlap and create pockets particularly rich in fuel. In suchregions combustion of the fuel is incomplete and soot particles areformed. This is an undesirable effect for both the engine and itsoperating environment. It is an object of the present invention toprovide means for suppressing the formation of soot by promotingcomplete combustion of the fuel.

SUMMARY OF THE INVENTION

This invention therefore provides a method and apparatus for directing ajet of air into the plume overlap region to disperse fuel-rich mixturetherein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference, byway of example only, to an arrangement illustrated in the accompanyingdrawings.

FIG. 1 shows a cross-sectioned view of an annular combustion chamberassembly and plenum region separated by an annular heat shield

FIG. 2 shows a second embodiment of the annular heat shield wherein theheat shield includes a plurality of abutting segments, with only aportion of the abutting segments illustrated

FIG. 3 shows a cross sectional view of an annular combustion chamberassembly along line 3--3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An annular combustion chamber assembly as in FIG. 1 comprises an annularinner casing 1 and a concentric outer casing 2. At their upstream endsthe inner casing 1 and the outer casing 2 converge to form the head ofthe chamber in the shape of an annular cowl 3. The cowl is formed with aplurality of openings 4 at its foremost point. In operation, openings 4create a source of high pressure air because they receive a flow of airfrom the high pressure compressor. The cowl 3 has a plurality of furtheropenings circumferentially distributed in the outer wall.

An annular end wall 30 includes bulkhead 6 extending between the innercasing 1 and the outer casing 2, downstream of the cowl 3. The bulkhead6 and the cowl 3 define a plenum region 7 in the head of the chamber.Downstream, the bulkhead 6, inner casing 1 and outer casing 2 define acombustion chamber 8. The downstream face of the bulkhead 6 is protectedfrom the high temperatures generated in the combustion chamber 8 duringoperation by an annular heat shield 9 which is secured to the bulkhead6.

In one embodiment (FIG. 1), heatshield 9 comprises a single continuousring with a plurality of raised ridges 10 extending from the upstreamface and contacting with the downstream face of the bulkhead 6. Anetwork of passages 11 is thus defined between the bulkhead 6 and theheat shield 9. The bulkhead defines a plurality of metering holes 12which communicate between the plenum region 7 and the network ofpassages 11. The raised ridges define a plurality of openings 32 at theradially inner and outer edges of the heat shield annulus 9, such thatthe passages 11 communicate with the combustion chamber 8. In analternative configuration (FIG. 2) the heat shield 9 comprises aplurality of sector-shaped segments 13, as in FIG. 2. The abutting edgesof adjacent segments are aligned radially with respect to thelongitudinal axis 22 of the engine. This configuration would alsoprovide raised ridges 10 on the upstream faces of the segments 13 andhence a network of passages 11 between the bulkhead 6 and the heatshield 9.

The bulkhead 6 also defines a plurality of first entry apertures 14distributed at regular intervals around the annulus. The heat shield 9defines a plurality of slightly larger first exit apertures 15,positioned to line up with first entry apertures defined by the bulkhead6.

The combustion chamber 8 receives therein a plurality of airsprayburners. Each airspray burner comprises a hollow arm 16, secured to theengine outer casing 17 and extending inwards through an opening 5 in thecowl 3 into the plenum region 7. A generally cylindrical hollow head 18extends distal to the arm 16 through first entry apertures 14 in thebulkhead 6 and first exit apertures 15 in the heat shield 9 to encroachslightly into the combustion chamber 8. The downstream end of the head18 is fitted tightly into a ring 19. The ring 19 has a lip at itsdownstream end which locates on the heat shield 9.

When the engine is in use a portion of the flow of air from the highpressure compressor enters the plenum region 7 through the openings 4 inthe cowl 3. Some portion of the air flowing into the plenum region 7enters the network of passages 11 through the metering holes 12 in thebulkhead 6. The air flowing through the passages 11 cools the heatshield 9 and eventually passes into the combustion chamber 8 throughopenings 32 at the inner and outer edges of the heat shield annulus 9.

Some further portion of the high pressure air flowing into the plenumregion 7 enters the head 18 of the airspray burner. The airspray burnerswirls and mixes the flow of air with fuel supplied through the hollowarm 16 and discharges the mixture into the combustion chamber 8. Themixture spreads into the combustion chamber 8 as a plume. At some pointdownstream adjacent plumes overlap to create fuel-rich pockets. Withinthese pockets combustion of the fuel is incomplete and soot particlesare formed. However, the invention provides means for directing a jet ofair into the overlap region to disperse the fuel-rich mixture andencourage complete combustion.

According to the preferred embodiment of the invention a plurality ofsecond entry apertures 20, preferably a plurality of slots 20, aredefined by the bulkhead 6 and a corresponding plurality of second exitapertures 21, preferably a plurality of slots 21 are defined by the heatshield 9, as in FIGS. 2-3. Slots 20 and 21 are radially aligned withrespect to the longitudinal axis 22 of the engine. Slots 21 in the heatshield 9 are aligned with but slightly larger than slots 20 in thebulkhead 6, such that a clear unobstructed path is provided between theplenum region 7 and the combustion chamber 8. Each slot 20 and 21 ispositioned equidistant from two adjacent airspray burner heads 18.Furthermore each slot intersects a straight line between the centerpoints 24 of the two adjacent airspray burner heads 18 which flank theslot. In the embodiment of FIG. 1, the slots 20,21 are formed in thebulkhead 6 and heat shield 9, respectively. In the embodiment of FIG. 2where the heat shield 9 includes abutting segments 13, a portion of eachof the second exit aperture (slot 21) is formed in an edge of thesegment 13 so that a complete slot 21 is formed by abutting adjacentsegments 13.

When the engine is in use, that portion of the high pressure airentering the plenum region 7 which does not enter the airspray burnerheads 18 or the cooling passages 11 flows instead through slots 20 and21 directly into the combustion chamber 8. The slots 20 and 21 provide adirect unobstructed path from the plenum region 7 into the combustionchamber 8, such that the air flow therethrough does not suffersignificant momentum losses. The size and shape of slots 20 and 21ensure air passing therethrough enters the combustion chamber in theform of fan-shaped jets. Furthermore, the position of slots 20 and 21relative to airspray burner heads 18 ensures the jets are directedaccurately into plume overlap regions. Consequently, jets impinge uponoverlap regions and retain sufficient energy to have the necessarydispersal effect on the fuel-rich mixture therein. Thus, the jets ofhigh momentum air promote complete combustion of fuel and suppressformation of soot particles.

We claim:
 1. A combustion chamber for a gas turbine engine comprising:acombustion chamber having an annular end wall, the end wall defining anupstream end of the chamber and having first entry and exit aperturesand second entry and exit apertures; a plurality of fuel injector means,associated with the first entry and exit apertures, for introducingplumes of a fuel and air mixture into the combustion chamber, the plumesbeing capable of overlapping; and a source of high pressure air on theupstream side of the end wall communicating with the first and secondentry and exit apertures, the second entry and exit apertures directingthe high pressure air into and dispersing overlapped plumes; wherein theend wall comprises an internal bulkhead and a heat shield spaced fromthe bulkhead, the second entry apertures are located in the bulkhead andthe second exit apertures are located in the heat shield co-axiallyaligned with the second entry apertures in the bulkhead.
 2. A combustionchamber according to claim 1 wherein said combustion chamber is of anannular configuration defined by an inner circumferential wall and anouter circumferential wall and the annular end wall, and the injectormeans for introducing fuel-air mixture are spaced apartcircumferentially around the chamber.
 3. A combustion chamber accordingto claim 1 wherein the second entry and exit apertures are slots suchthat said jets of air issuing from said slots are fan-shaped.
 4. Acombustion chamber according to claim 3 wherein said slots are radiallyaligned with a longitudinal axis of the engine.
 5. A combustion chamberaccording to claim 1, wherein the heat shield comprises a plurality ofcircumferentially abutting segments, each segment having edges abuttingedges of an adjacent segment, each edge including a portion of a secondexit aperture so that a complete second exit aperture is formed byabutment of adjacent segments.
 6. A combustion chamber according toclaim 5, wherein said second entry and exit apertures are radiallyaligned with the longitudinal axis of the engine.
 7. A combustionchamber according to claim 1, wherein the second apertures areequidistant from adjacent first apertures.
 8. A combustion chamberaccording to claim 7, wherein the second entry and exit aperturesintersect a straight line between centers of the first entry and exitapertures.
 9. A combustion chamber according to claim 1, wherein thesecond entry aperture is smaller than the second exit aperture.